Investigaciones sobre coherencia en concepciones y creencias del profesorado

The World Energy Council has estimated that 2 terawatts of energy can be generated by wave power. Since waves have the potential of providing a surplus of energy sources, different forms of generates have been designed to maximize energy output from different bodies of water. The most popular and known such technology is hydroelectric power. Hydropower uses running water to propel turbines, which in turn runs an electric generator to create electricity. This is considered a renewable technology since the „fuel‟ that is used, water, can easily be replenished through the water cycle. The only cost that comes with a hydroelectric dam is the construction and operation of the generator facilities.

Common types of hydroelectric power plants use dams to store water from rivers or streams in a reservoir. The collected water is fed to the turbines through small canals. The electricity production can vary during the day, but is generally higher during the day. Because the generated power is low, some power plants, also known as pumped storage plants, pump the used water back into the reservoirs at night.

These damns, such as the Hoover Dam in Nevada, and the Grand Coulee Dam in Washington, also meet societal needs such as irrigation, flood control and recreation.

Hydropower accounts for about 19% of electric generation. In the US, hydroelectric plants, which have the capacity of 100,000 megawatts, provide about 3.25% of the nation‟s total energy and about 6%

of America‟s electricity. Hydroelectric power also makes up about 63% of renewable electricity in the US. In a current study by the U.S. Department of Energy, existing dams can provide 12,000MW of

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additional capacity, and if new installations are made such that include the use of tidal current and tidal waves, hydroelectric power could provide up to 15% of America‟s electricity by 2030.

Other types of water energy technologies include run-of-the-river, Tidal Barrage, and the use of ocean waves. In the run-of-the-river plants, no reservoirs are created, but instead the energy flow of the river is used. Electricity is generated by the natural flow of the river, and fluctuates depending on the cycle of the river. It can be used for large scale power, but mostly kept to capabilities less than 30MW.

This is popular in China, but has potential in many other countries, such as the United States.

Tidal barrages are similar to hydroelectric dams, except they are larger and are placed at the entrance of a bay or estuary. The retained water is released through the turbines which generate the electricity. In order for the barrage to work economically, the range between high and low tide must be near ten feet. The largest and oldest tidal barrage in the world is the La Rance estuary in Northern France, which was built in 1966 and has the capacity of 240MW.

There are several methods in creating electricity from waves. One of them is using the air

produced by waves. Figure 36 below, represents how a water turbine can use the water‟s wave to generate energy.

Figure 36: The Workings of a wave power station Wave Power http://people.bath.ac.uk/as474/wavepower.html

At a wave power station, the waves cause the water in the chamber to rise and fall which causes the air in the chamber to pass in and out from the top of the chamber. This airflow will turn a turbine, which will turn an electric generator, thus creating electricity. Another method is through the use of the natural movement of the waves. Here a float on a buoy follows the up and down wave motion, causing the attached plunger to move in the same direction. The plunger‟s movement causes the attached hydraulic pump to change the vertical movement into a circular motion. This then drives an electric generator to produces electricity that is sent to shore through submerged cables.

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While there are many advantages to using water energy, there are also many disadvantages. For example, studies have shown that large reservoirs can emit as many greenhouse gases as a fossil fuel power plant. At the beginning of a damn‟s life, flooded vegetation can decompose, which releases methane and carbon dioxide gases. Dams can harm the river‟s ecosystem, changes the water temperature, dissolve the oxygen and other nutrients in the water which can kill aquatic animals. Tidal Barrages are usually built in delicate estuary ecosystems, which can have a huge environmental impact on marine animals. Run-of-the-river is also very dependent on the flow of the water. Such things as prolonged droughts may diminish the water level in the river, which lowers electricity generation.

While using the earth‟s water has a few drawbacks, it is clear that it is possible to use it to produce electricity. In figure 37 below, the use of worldwide hydroelectric dams to produce electricity is seen. As was stated before, about 6% of U.S. electricity is created by hydroelectric dams. Yet in places like Norway, 99% of their electricity is created by falling water. This clearly shows that it‟s definitely possible to stop using fossil fuels to create our electricity.

Figure 37: Percentage of electricity from hydroelectric dams http://css.snre.umich.edu/css_doc/CSS03-12.pdf

(Source: University of Michigan)

The Bay of Fundy in Nova Scotia, Canada has one of the highest tidal ranges in the world. The Bay of Fundy has the tide spring range of 14.5 meters with an extreme range of 16.3 meters. This means about 100 billion tons of seawater moves in and out of the bay each day. With this much tidal power, engineers and scientists have been looking for different ways to harness this power into renewable energy.

The Electric Power Research Institute estimates that there are about 50,000 megawatts of energy that can be generated by the tidal force in the Bay of Fundy. Three hundred megawatts would just be

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developed by the Minas Passage alone which would be enough to displace over one million tons of greenhouse gasses per year. That‟s like removing 200 thousand cars off the road.

There are several different turbine units that are being developed to harness the tidal energy with minimal environmental impact. Such designs can be seen in Figure 38 through 41 in the next page. At the heart of each one of these deigns is a TGU, or Turbine Generator Unit, which can be seen in Figure 38.

The TGU works the same way a wind turbines work, with the foils rotating a permanent magnet generator that creates electricity. The big difference between this and the wind turbines is that water is 800 times denser than air and thus the TGU‟s provide more power. Each TGU has a generating peak output of about 180kW.

These TGU‟s can then be used in different designs. One design is seen in Figure 39 is the RivGen Power System, which is specially made to generate electricity at small river sites. They typically would be connected to diesel generators, and then turned off when the RivGen begins producing electricity. This can generate up to 50kW in a 10 foot per second river current. Other designs can be seen in Figure 40 and 41, that represent the TidGen and the OCGen Power System, which are designed to be used in water depth of 50 and 80 feet respectively.

In 2008, ORPC, or the Ocean Renewable Power Company, was the first company to generate electricity from the Bay of Fundy tidal currents without the use of dams. The reason dams are not used in the Bay of Fundy is from the fear that A beta pre-commercial version of the TidGen power system was deployed in the Bay of Fundy and met or exceeded all expectations and is the largest ocean energy device to ever be deployed in the US.

Another powerful water source of energy is the stream of the Gulf of Mexico. With a flow rate of about 8 billion gallons of water per minute, it is capable of generating between four to ten gigawatts of power, which is about the same amount of energy produced by four to ten new nuclear power plants. Just harnessing 1/1000 of the Gulf‟s steam available energy would power about seven million homes and business. This is equivalent to 1/3 of the electricity used in the state of Florida. These underwater turbines could generate up to four times the power that can be generated by wind turbines with the same

generating capacity. As explained earlier, the turbines have about an 85% to 90% capacity factors that equal to natural gas and coal plants, but have no CO2 emissions. Each 1.2MW turbines installed would save about 10 thousand tons of CO2 from being omitted to the air. If around ten thousand of these turbines are created by 2013-2014, it would cut down CO2 emissions by 100 million tons and save the U.S. three billion dollars.

One of the many designs that could be implanted to harness the gulf's stream power is to have turbines over 1000feet under the surface. One of the big issues with this design is the "Cuisinart effect", which is where fish could get close to the turbines and be sliced. When this occurs, the blood could attract

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other fish and the process would repeat. While this is a worry for some environmentalists, the probability of this happening is very low, since the turbines are turning so slow. With the slow momentum of these turbines, the likelihood that the fish will get caught and killed is low.

Using water as a renewable energy is one of the best and most reliable resource. With the earth covered in over 70% of water, using water as a resource for renewable energy is the most promising way to go. Unlike solar and wind energy, water energy is something that can be used day and night, and does not depend on high wind speeds.

Figure 38: Turbine Generator Unit

http://www.orpc.co/orpcpowersystem_turbinegeneratorunit.aspx (Source: Ocean Renewable Power Company)

Figure 39: RivGen Power System

http://www.orpc.co/orpcpowersystem_rivgenpowersystem.aspx

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Figure 40: TiGen Power System

http://www.orpc.co/orpcpowersystem_tidgenpowersystem.aspx

Figure 41: OCGen Power System

http://www.orpc.co/orpcpowersystem_ocgenpowersystem.aspx

(Source: Ocean Renewable Power Company) South Korea

South Korea is one of the most promising countries for the application of the tidal energy generation. Tocardo International, which is the leading producers of hydro-power turbines, has agreed to sell its renewable energy in South Korea. It is the only company in the world that produces and sells commercially viable water turbines. These turbines are market-ready and can generate energy in any environment with flowing water such as offshore tidal currents or in-shore rivers.

Some of these turbines include the 100kW T100 turbine, the 200kW T200, which are available commercially. Other models such as the 500 kW and 1MW turbines are expected to be ready by 2013 and 2015 respectively. The T100, which can be seen in Figure 42 below, is the smallest Turbine this company has and it is ideal for river and inshore application. It operates in a minimal depth of 4 meters

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and has a life expectancy of 20 years. The turbine has two blades that control a 14 pole permanent magnet and produces up to 100kW. There is currently a T100 turbine in use at the Den Oever Inshore Project site in the Netherlands. This turbine has been feeding electricity into the grid since the summer of 2008. The turbine has the capacity of 35kW and produces electricity for about 12 households. The project in the Netherlands can be seen in Figure 42.

Figure 42: T100 Turbine

http://www.tocardo.com/digi_cms/58/products.html

(Source: Tocardo International)

Figure 43: T100 Turbine in Den Oever

http://www.tocardo.com/digi_cms/44/den-oever-inshore-project.html

(Source: Tocardo International)

Another turbine is the T200, which is a medium sized turbine more suitable for inshore and near shore tidal applications. It is small enough to be attached to existing civil structures such as brides or barrages, as can be seen in Figure 44. The blade diameter for this turbine is a lot larger than the T100‟s and it has a 20 pole permanent magnet generator. This figure is from the Oosterschelde Inshore Project in

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Oosterschelde, Netherland where five T200‟s are expected to be installed later this year. This project site will have the capacity of 1MW and will produce electricity for about 350 households.

Figure 44: T200 Turbine in Oosterchelde, Nertherlands http://www.tocardo.com/digi_cms/61/t200.html

(Source: Tocardo International)

The T500 is specially designed for offshore tidal currents and has blades that are much larger than the T200 or T100. This turbine is in its final stages of development and is expected to hit the market by 2013. The T500 can operate at depths of 5.5 to 25 meters. The last type of Turbine Tocardo is developing is the T1000, which is designed for heavy duty offshore projects. It has a rated power of about 1MW and is expected to be developed by 2015.

Figure 45: T500 Turbine size

http://www.tocardo.com/digi_cms/62/t500.html

(Source: Tocardo International)

87 KOMIPO

Two companies, Luna Energy and the Korean Midland Power Co (KOMIPO) are looking to create a colossal 300 turbine field in the Wando Hoenggan Water Way off the South Korean coast by 2015. These Turbines, as seen in Figure 46, would provide up to 300 MW of renewable energy, which is enough energy to power up to 200 thousand homes. Each turbine is a generator that provides 1MW and is about 11.5 meters in diameter. It is predicted to be a 500 million Euro dollar project, and will use the fast-moving tidal steams to turn the turbines on the sea floor. Each turbine will be about 60 feet high with a 2500 ton frame that contains a pump, generator, motor and electronics. The ecological impact of the field is expected to be less than that of tidal barrages.

Figure 46: 1MW KMOIP Tidal Turbine

http://www1.eere.energy.gov/water/hydrokinetic/information.aspx?type=tech

(Source: U.S. Department of Energy)

Figure 47: KMOIP Turbine Field http://infranetlab.org/blog/tidal-turbines

(Source: Infrastructure Networks Library)

88 Sihwa Lake Tidal Power Station

Located about 20km south of Incheon and South Korea, this tidal power plant currently holds the highest-capacity power outage in the world. Its capacity of 254MW surpasses the previous record-holder of 240MW from the Rance Tidal Station in northwest France. In 1994 when the government attempted to create a freshwater lake, a 7.9 mile dam was created and the tidal power plant was proposed as a way of cleaning the water. This power station is expected to reduce 315,440 metric tons of CO2 per year. This station features a sea wall that stores the water during high tide, but only generates power from incoming tides. It has a diameter of 7.5 m and was completed in early 2010. A picture of the generator turbine can be seen in Figure 48. This plant is expected to reduce the effect of CO2 by 315,000 tons and since it began operation is early 2011, it has produced 552.7GWh of energy annually.

Figure 48: Sihwa Lake Tidal Power Station

http://wordlesstech.com/2011/04/30/sihwa-tidal-power-plant-in-ansan-near-completion/

(Source: Wordless Tech)

Figure 49: Sihwa Lake Tidal Station Motor

http://wordlesstech.com/2011/04/30/sihwa-tidal-power-plant-in-ansan-near-completion/

(Source: Wordless Tech)

89 Future Power Stations

Under the national slogan of Green Growth in South Korea, it adopted a nationwide Renewable Portfolio Standard. This standard requires utility companies to generate a certain portion of energy from renewable resource, from about 2% in 2012 to about 8% in 2020. This is why South Korea has come up with a plan of mega-scale tidal power generation. This means that off the shore of South Korea many more tidal power plants are expected to be built, like can be seen in Figure 50.

Figure 50 South Korea Plans for Tidal Power Plants

http://nautilus.org/napsnet/napsnet-special-reports/south-koreas-plans-for-tidal-power-when-a-green-solution-creates-more-problems/

(Source: Nautilus Institute)

Two of these proposed locations for the tidal plants are the Incheon bay and the Ganghwa way, better seen in the Figure 53. The Incheon Bay would have a capacity of 1,320MW, more than five times the power from the Sihwa plant. This project is expected to be equipped with 44 turbines and meet 4.5%

of the nation‟s household electricity needs. Construction on this plant is scheduled to begin in 2014 and be completed by the end 2019. The Ganghwa Tidal Power Plant would have the capacity of 420 MW, and be 65% larger than the Sihwa plant.

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Figure 51: Proposed Incheon Bay and Ganghwa tidal power plant locations

http://nautilus.org/napsnet/napsnet-special-reports/south-koreas-plans-for-tidal-power-when-a-green-solution-creates-more-problems/

(Source: Nautilus Institute)

While there is a larger amount of renewable electricity coming from these plants, many local communities are protesting against the building of these plants. Locally, the plants could destruct

ecosystems, decline local fisheries and eliminate jobs, increase the fish of flooding, and impact the natural landscape. On the National scale, it would be a large initial cost for the construction of these tidal plants, with an estimated cost of $3.4 billion. The endangered species‟ population could decline from the tidal processes in the Yellow Sea.

The idea of decreasing fossil fuel consumptions and use renewable energy is great, but by creating these gigantic Tidal Power Plants that could severely harm the ecosystem, and might create problems for South Korea.

While it‟s true that applying these larger power plants could harm the ecosystem, I think it‟s more important to build these power plants. It is important to start using renewable resources and to stop relying on non-renewables such as nuclear and oil. I think that while short term it might seem that this would harm the environment, long term it would help it.

91 Bay of Fundy

The Bay of Fundy is a very promising site for renewable energy. Because of its large tides that can go up to 16m in some places, it has potential to produce a large amount of tidal current energy. Chignecto Bay and the Minas Basin form two arms at the head of the Bay and have exceptional high tides. At high tide, huge volumes of water in the bay floods into the rivers, with the water racing in speeds close to 10mph.

This generates rapids that are between 3 to 3.5 meters high.

Figure 52: Google image of Minas Basin and Minas Passage http://maritimetidal.com/?page_id=38

The Bay of Fundy‟s surface current can reach up to 10 knots, which is equivalent to s speed of 5.1 m/s at peak surface during high tide. Each tide lasts around six hours, while high and low tides both peak for about an hour. Given that the change of tides can last for half a day, it is possible to harness the constant change and generate energy.

The Minas Passage and Minas Basin, as seen in Figure 52, have the strongest current in the Bay of Fundy running at an average current speed of 3.28m/s. The narrowest part of the Minas Passage is 4.5 to 6.5 km wide, which dumps into the Minas Basin. The Minas Basin has an even stronger current, at

The Minas Passage and Minas Basin, as seen in Figure 52, have the strongest current in the Bay of Fundy running at an average current speed of 3.28m/s. The narrowest part of the Minas Passage is 4.5 to 6.5 km wide, which dumps into the Minas Basin. The Minas Basin has an even stronger current, at